Greek Astronomy

The Revival of an Ancient Science

One of the most powerful creations of Greek science was the
mathematical astronomy created by Hipparchus in the second
century B.C. and given final form by Ptolemy in the second
century A.D. Ptolemy's work was known in the Middle Ages through
imperfect Latin versions. In fifteenth-century Italy, however,
it was brought back to life. George Trebizond, a Cretan emigre
in the curia, produced a new translation and commentary. These
proved imperfect and aroused much heated criticism. But a German
astronomer, Johannes Regiomontanus, a protege of the brilliant
Greek churchman Cardinal Bessarion, came to Italy with his
patron, learned Greek, and produced a full-scale "Epitome" of
Ptolemy's work from which most astronomers learned their art for
the next century and more. Copernicus was only one of the
celebrities of the Scientific Revolution whose work rested in
large part on the study of ancient science carried out in
fifteenth-century Italy.

In the thirteenth and fourteenth centuries, a number of recent
Arabic and Persian astronomical works were translated into Greek
by scholars who traveled to Persia under the Ilkhanid Empire.
One short and confused treatise, translated by Gregory
Chioniades, describes Tusi's lunar theory, illustrated, not
altogether correctly, in this figure along with Tusi's device for
producing rectilinear from circular motions (shown also in
Vat. ar. 319 (math19)).
A part of the planetary and lunar theory of
the astronomers of Maragha was later utilized by Copernicus,
though scholars do not know how he gained access to this
material.

George Trebizond, one of the notable Greek scholars who came to
Italy in the early fifteenth century, made a new translation of
the "Almagest" from the Greek for Pope Nicholas V between March
and December of 1451. Due to a dispute about the quality of
Trebizond's commentary on the text, the translation was never
dedicated to Nicholas. This very elaborate manuscript of the
translation, with the figures drawn in several colors, was
dedicated to Pope Sixtus IV by George's son Andreas. These pages
show Book VI Chapter 7, on the computation of the duration of
solar and lunar eclipses.

During the same nine months that George Trebizond made his
translation of the "Almagest," he also wrote a commentary as long
as the original text. The commentary was severely criticized,
however, which resulted in a falling out with Pope Nicholas V.
This opulent manuscript was dedicated to Pope Sixtus IV by
George's son Andreas along with Vat. lat. 2055 of the
translation. These pages contain a large figure of the model for
the planet Mercury, shown at its least distance from the earth,
with a list of Mercury's parameters and distances, and then the
beginning of the treatment of Venus in Book X.

Nasir ad-Din at-Tusi was among the first of several Arabic
astronomers of the late thirteenth century at the observatory of
Maragha in Persia who modified Ptolemy's models based on
mechanical principles, in order to preserve the uniform rotation
of spheres. This early Arabic manuscript contains his principal
work on the subject, the "Tadhkira fi ilm al-Haya" (Memoir on
Astronomy). The figure shown here is his ingenious device for
generating rectilinear motion along the diameter of the outer
circle from two circular motions.

The "Epitome of the Almagest" was written between 1460 and 1463
by Georg Peurbach and Johannes Regiomontanus at the suggestion of
Cardinal Bessarion. It gave Europeans the first sophisticated
understanding of Ptolemy's astronomy, and was studied by every
competent astronomer of the sixteenth century. The illustration
here shows the distance of the sun from the earth as 1210
terrestrial radii (about 4,800,000 miles), which is too small by
a factor of twenty, but gives a solar parallax (the maximum
displacement due to observing the sun from the surface rather
than from the center of the earth) of less than 3 minutes, still
well below the limit of observational accuracy.

Ptolemy's "Geography" contains instructions for drawing maps of
the entire "oikoumene" (inhabited world) and particular regions,
along with the longitudes and latitudes of about eight thousand
locations in Europe, Africa, and Asia. The maps in manuscripts
of the "Geography," however, date only from about 1300, after the
text was rediscovered by Maximus Planudes. There are two
versions, the A recension with twenty-six large regional maps,
and the B recension, displayed here, with sixty-four smaller
regional maps and four large additional maps. Shown here is the
additional map of Europe which reveals Ptolemy's systematic
exaggeration of west to east distances, particularly in the
eastward extension of Scotland and the west to east slope of
Italy.